Glass having low power factor



Patented Sept. 14, 1948 m -era s rar orrie-2e Corning Glass Work 'poratiori of New York s, Corning, Y a cor- No Drawing. Application .January. 23,..1-945, Serial No. 574,204

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This invention relates to glass compositions and has for its pr mary object to provi e ne and useful glasses having certain'special characteristics making them suitable as an insulating medium for conductorscarryingradio frequency currents. As examples of such uses my new glasses-are part cularly-suitable for the insulating laminae in electrical condensers and for sealing'iron conductors into tubes and envelopes of electronic devices. 'Mica, which has heretofore been used for insulating such condensers, is 'very expensive "and requires considerable selection to insure suitable" uniformity in quality. Glass, on the'other-han-d, can bemanu'factured relatively cheaply -and'with great uniformityin composition-and properties. However, no glass heretoforerhas been devisedwhichcornbines the desired characteristics to the extent that does the glass to be-hereinafter described.

' The desired "characteristics are:

A; power factor less than 406%, as measured at eh'frequency of one mega'cycle atr-room temperature. The power factor of dielectrics employed in high frequency circuits is veryimportant'and withra'diofrequencies the powerless is objectionably large unless the power "factor -is ,as low as 116% -or less.

A 'dielectric'constant of at least 7 or 8.

A temperature *coefficientfor dielectric constantless-than 200'parts per-million per degree C.,is required to-meet the Army-Navy specifications for 'fixed, mica-die1ectric capacitors having extremelylowpowerfactors and adapted for use with relatively large currents. For other purposes, the temperature coefficient may be higher. By temperature coefficient is meantthe rate of change of-dielectric constant with change of'temperature.

A softening temperature not greater than 625 C. ln:order'to pennit fusingand sealing the contiguous;edges,ofcsuperposed laminaeof the glass without -,fusing intermediate metallic laminae. Softening -temperature is defined 1 in ;an article entitled A ;method for'measuring the softening temperature 1of glasses, by J. II. :Littleton; Jour. Am. Cer. 80.0., .vol. 10, page '259 (1927).

A linear coefficient of thermal expansion in the neighborhood of l28;x 10 .centimeters per centimeter per degree C. is desirablefor some purposes, such as, glass-to-metal seals with iron. Lower expansion coefiicients are desirable for other-purposes.

and all of these, properties "may 'easily be obtained at the sacrifice of others and many glassesa're known which havelowpowerfactors but they lack oneiormore'of the'above mentioned properties and hencehave. not been entirely suitable for the purposes in view. The problem solved by me.has been to obtain all of the desiredpropertieslin .one glass.

IIt'iscommonly believed;that alkali, metal '01:- ides 'in glass are generally detrimental to the electrical properties fof theglass, such as power factor, and that theyshould'be omitted or'kept toaminimum if low power factors and other valuable electrical characteristics are to .be obtained." It is. also known that glasses having very high Silica contents, in the neighborhood of 8 02, have exceptionally w power factors. Moreover, my prior researches have shown that the usually low power factors of some alkali-free glasses can still further be lowered by the lntroduction of alumina. In other words, past experience indicates-that high silica, low alkali and high alumina contents are conducive to low power factors. 'Howeventhey also result in high-softening temperatures.

.In my pending application Serial No. 558,278 filed October 11, 1944, now Patent No. 2,431,980 granted Dec. 2, 1947,'it is shown that thesegeneralizations do-not hold true for glasses containing lead oxide and the alkali metal oxides, but that :the .presencepfalumina and a high :silica contentiaregdetrimental touthe power factor of suchglasses. Hence it; is "showntthat such glasses possess all of the above mentioned desirable properties, provided thatsilica does not exceed 50%, alumina is absent andsoda, potash and lithia are present in the proper ratios.

In another application, Serial No. 574,203 filed concurrently "herewith and issued January '21, 1947 as .Patent No.:2,414,504, I have shown that similar 'glasses containing BaO .inlieu of.PbO also possess the-above mentioned desirable properties.

I havefound that" the above properties. are:also possessed by glasses which consist essentially of SiOz, BaO, PbO, K20, NazO and"LizO,'the SiO9 being less than'6 5%; thertotal of the alkalimetal oxides '(RzO) being'morethan 5% and not'less than (5+X) whereX is the excess of'flSiOz over 4 5% -the ratio'KzQ/N 21.20 being from 1L5/1to- 4/1, the ratio jKz+-Nazo) /LizO-bei ng from 4/ 1 -'to I9/1ythe "total *BaOand PbO-belngbet-ween 10 3 and 60% and the ratio of BaO to PhD being less than 1 when the S102 is below 40%, the glass being substantially free from A1203. The lowest power factors are obtained when the ratio KzO/NazO is about 2.3/1 and the ratio (KaO+Na20) /Li20 is about 9/1. There is no definite upper limit for the total content of alkali metal oxides, but on account of the approach of instability and for other practical reasons I prefer to use not more than a total of about 25% thereof. With a total alkali metal oxide content around 17% to 21%, glasses having very high expansion coefficients and low power factors can be produced which are particularly suitable for forming glass-to-metal seals with iron. The presence of small amounts of boric oxide does no harm but has no advantage except when it is desired to lower the expansion coefiicient. If desired, the power factor and softening temperature can be lowered somewhat further by the introduction of fluorine, preferably as an alkali fluoride.

As pointed out above, the total alkali content must be not less than (5+X) where X is the excess of silica over 45%. To illustrate the criti-- cal effect which alkali metal oxides and also the presence of alumina have on the power factors of my new glasses, the following comparative compositions in percent by weight and their respective power factors are shown in Table I below. Glass A is a barium-lead glass in which R20 is less than (5+X) and which contains alumina. In glass B the S102 and R20 were altered sufficiently to make R20 slightly more than (5+X). The result of this was to lower the power factor by an amount equal to about 24% of its original value and to make the glass suitable for my purpose. In glass C the omission of alumina brought a further lowering of the power factor by another 5%.

Table I S10 58. 2 54. 2 55.2 PbO 20. 20. 5 20. 5 BaO..-.. 7.5 7. 5 7. 5 K20 8.8 11.6 11.6 NazO 3.0 3.9 3.9 L110 1.0 1.3 1.3 .4120; 1.0 1.0 Power Factor, percent... .076 058 .054 (5+X) 18. 2 14. 2 15. 2

InTable II examples of glasses falling within my invention and calculated in percent by weight from their respective batches, together with their properties, are given:

About 1% of SbzO; was introduced into the batches for the purpose of fining the glasses. This had no substantial effect on their properties. The values for power factor were measured at a frequency of one megacycle by the method known as ASTM D--42T, set forth on page 1148 et sq., part III of the ASTM Standards for 1942.

It will be noted that the power factors of the above glasses are substantially below .06% and that their other properties are also suitable for the purposes set forth above. Glass 5 illustrates the effect of adding fluorine to glass 4 and the power factor and the softening point were thereby substantially reduced. Glasses 4and 5 are particularly suitable for insulating laminae in lieu of mica in large-current, fixed condensers or capacitors. Glass 3, which has an expansion coefiicient near that of iron, is particularly useful as an iron-sealing glass in the manufacture of glass-to-metal seals.

I claim:

1. A glass having a power factor less than .06%, a dielectric constant of at least 7 and a softening temperature less than 625 C., which consists essentially of S102, BaO, PbO, K20, NazO, and L120, the S102 being more than 38% and less than 65%, the total of the alkali metal oxides being more than 5% and not less than (5+X) where X is the excess of $102 over 45%, the ratio KzO/NazO being from 1.5/1 to 4/ 1, the ratio (K20'+Na20)/Liz0 being from 4/1 to 19/1, the total BaO and PbO being between 10% and 60%, and the ratio of BaO to Pb0 being less than 1 when the S102 is below 40%, the glass being substantially free from A1203.

2. A glass having a power factor less than .06%, a dielectric constant of at least '7 and a softening temperature less than 625 C., which consists essentially of SiOz, BaO, PbO, K20, NazO and LizO, the Si02 being more than 38% and less than 65%, the total of the alkali metal oxides (R20) being more than 5% and not less than (5+X) where X is the excess of Si02 over 45%, the ratio KzO/NazO being about 2.3/1, the ratio (K20+Na20)/Li20 being about 9/1, the total BaO and Pb0 being between 10% and 60 and the ratio of BaO to Pb0 being less than 1 when the S102 is below 40%, the glass being substantially free from A1203.

3. A glass having a power factor less than .06%, a dielectric constant of at least '7 and a softening temperature les than 625 C., which consists essentially of S102, BaO, PbO', K20, NazO, and L120, the S102 being more than 38% and less than 65%, the total of the alkali metal oxides being from 5% to 25% but not less than (5+X)% where X is the excess of S102 over 45%, the ratio K20/Na20 being from 1.5/1 to 4/1, the ratio (K20+Na20) /Li20 being from 4/1 to 19/1, the total BaO and PbO being between 10% and 60 and the ratio of BaO to PbO being less than 1 when the S102 is below 40%, the glass being substantially free from A1203.

4. A glass having a power factor less than .06%, and an expansion coefflcient about 128x10 cm. per cm., per degree C., which consists essentially of SiOz, BaO, PbO, NazO, K20,

and L120, the 8102 being more than 38% and lessthan 65%, the total alkali metal oxides being from about 17 to about 21 the ratio KzO/NazO being from 1.5/1 to 4/ 1, the ratio.

being from 4/1 to 19/1, the total BaO and PbO 40%, the glass being substantially free from A1203.

5. A glass having a power factor less than .06 a dielectric constant of at least 7 and a softening temperature less than 625 C., which has the approximate composition 38% to 55% 5102, to 30% PbO, to BaO, 7% to 13% K20, 1.8% to 5.4% NazO and .5% to 2% Li20, the total of the alkali metal oxides being more than (5+X) where X is the excess of S102 over 45%,

the ratio K2O/Na20 being from 1.5/1 to 4/1 the ratio (K2O+Na2O)/Li2O being from 4/1 to 19/1 and the glass being substantially free from A1203.

6. A glass having a power factor less than .06%, a dielectric constant of at least 7 and a softening temperature less than 625 C., which has the approximate composition 45% Si02, 10% PbO, 25% BaO, 12.6% K20, 5.4% Na2O, and 2.0% U20.

7. A glass having a power factor less than .06%, a dielectric constant of at least 7 and a softening temperature less than 625 C., which has the approximate composition SiO2, 30% PbO, 20%. BaO, 7% K20, 2.5% Na2O and .5% L120.

8. A glass having a power factor less than .06%, a dielectric constant of at least 7 and a softening temperature less than 625 C., which has the approximate composition 38% to 55% Si02, 10% to 30% PbO, 7.5% to 25% BaO, 7% to 13% K20, 1.8% to 5.4% Na2O, and .5% to 2% Li2O, the total of the alkali metal oxides being more than (5+X)% where X is the excess of S102 over the ratio K2O/Na2O being from 1.5/1 to 4/1, the ratio (K2O+Na2O) /Li2O being from 4/1 to 19/1 and the glass being substantially free from A1203.

WILLIAM H. ARMISTEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,018,816 Taylor Oct. 29, 1935 2,018,817 Taylor Oct, 29, 1935 

